Some phase-change materials have the ability to change colors and/or to reflect, block, or limit the transmittance of light at different wavelengths based upon changes in temperature and/or light absorbed by the phase-change materials. This facilitates the use of certain phase-change materials for certain light-blocking applications.
One type of phase-change material that has been studied for some time is vanadium oxide. Vanadium oxide is thermochromic material that has a variety of different oxide forms, including VO2 and V2O3. Vanadium dioxide, VO2, undergoes a reversible transition from a semiconductor phase (where the VO2 has a monoclinic crystal structure) to a metal phase (where the VO2 has a tetragonal crystal structure) at a critical temperature of about 68° C. The transitional phase change at this critical temperature results in the VO2 exhibiting a rapid change in electrical and optical properties. At this temperature-induced phase transition, VO2 acts as an optical “blocker” or barrier that substantially limits the transmittance of light at near-infrared (near-IR) wavelengths of about 1.2 micrometers.
Research has been conducted for exploring possibilities of utilizing vanadium dioxide in optical switching applications (e.g., as window coatings or optical shutters) due to its ability to limit the transmittance of light at near-IR wavelengths. In addition, certain dopants, such as tungsten and chromium, can be added to vanadium dioxide to lower its critical phase transition temperature to temperatures as low or even lower than room temperature (about 27° C.), thus enhancing the applications and environments in which vanadium dioxide may be used as an infrared light blocking material.
It would be desirable to provide an optical limiting material such as vanadium oxide or some other phase-change material that can be utilized as an optical switch to block or substantially limit the transmittance of light for a variety of different applications including light blocking applications at wavelengths shifted from the IR or near-IR range.